The need for a method and apparatus for submerging, entraining, melting and circulating a metal charge in a molten media has been vigorously pursued by a number of inventors over the last decade or so. Special attention has been directed to the problems attendant to the recycling of scrap aluminum that has a high surface-to-volume ratio which causes the scrap to float on the surface of the molten aluminum.
The inventor of the subject invention has provided a number of patentable solutions to this problem that have advanced the state of the art, as evidenced by the following patents to Raymodnd J. Claxton: Nos. 4,322,245 ('245('245); 4,386,764 ('764) and 4,592,658 ('658). These patents are variously directed to methods and apparatuses for submerging, entraining, melting and circulating a metal charge in a molten media.
Each of the Claxton Patents, i.e., '245, '764 and '658, describe and claim a novel impeller structure that creates a mild vortex in a molten media. The scrap aluminum charge is delivered into the mild vortex and entrained in the molten media for delivery to and through the novel impeller in such a way that a molten media circulation current is simultaneously developed.
The dual impeller vortex system of the subject invention advantageously allows one of the impellers to be operated continuously to maintain recirculation of molten media even at times when a vortex generating impeller is not being operated. This just described arrangement allows molten metal recirculation during such idle periods when scrap is not being charged. This is beneficial because during such idle periods there is no necessity of introducing agitation associated with vortex in order to maintain circulation.
There have been others that have sought to perfect vortex generation in scrap aluminum reclamation such as J. R. Gillespie in his patient U.S. Pat. No. 4,884,786 of Dec. 5, 1989 titled "Apparatus for Generating a Vortex in a Melt." Gillespie's invention is directed to an aluminum furnace having a charging well in which well an impeller rotates, but the impeller, instead of being supported on a complex framework and massive foundation, is suspended by means of a trolley from an overhead track. The well possesses a somewhat cylindrical configuration and includes both inlet and outlet ports, all arranged to complement a physical configuration of the impeller in establishing and maintaining a suitable vortex. A separate molten media circulation pump is provided in another region of the furnace to provide a circulation current in the molten media to drive molten media through the charging well.
The subject invention does not require a complex charge well wall structure as does Gillespie's but relies upon smooth vertical charge well walls and the cooperation of identical impellers positioned with one impeller inverted and the other impeller adjacent but beneath the one impeller.
Other patents of interest are the Ormesher U.S. Pat. Nos. 4,486,228 and 4,491,474 which, not unlike the Gillespie Patent, require a vortex generating impeller of a novel configuration cooperating with a uniquely configured charging well wall, whereas in the present invention only simple vertical charging well walls are called for.
Yet another patent of interest is the Wayle U.S. Pat. No. 4,893,941 directed to an apparatus for mixing viscous liquid in a container. The Wavle invention utilizes a pair of similar pumping impellers mounted on a single shaft one impeller above the other such that the impellers, when rotated, provide mixing of fluid in a container by positive multidirectionally controlled flow which is enhanced by interaction with walls of the container. Wayle, unlike the subject invention, is inherently incapable of creating a vortex or causing a circulation flow path to be generated independently by one of two impellers.